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Chapter 7

reinforcement, one should read the article by Rice [7.27]. Particulate reinforcement can be oxides, carbides, nitrides, borides, or even metals. Some of the common materials used are listed below:

The corrosion of most of these materials has been discussed in Chap. 5 (Corrosion of Specific Crystalline Materials) and will not be repeated here.

Actually, most of the ceramic products manufactured today could be considered ceramic particulate reinforced ceramic matrix composites. For example, one product not generally considered a composite by the ceramics community is MgO:carbon refractories. This product contains a substantial quantity of carbon particles in an effort to improve the corrosion resistance of the MgO in molten metal applications. In addition to the obvious oxidation of carbon to monoxide and/or dioxide, carbon will also react with MgO at temperatures above 1400°C forming magnesium vapor and carbon monoxide.

7.3 CERAMIC MATRIX COMPOSITES

Ceramic matrix composites are characterized by a high modulus of elasticity, excellent high temperature and corrosion resistance, but generally poor crack propagation resistance. The composite systems that have probably received the most attention are those of SiC or carbon fiber reinforced SiC. The major problem with these materials is one of oxidation of either the carbon or the SiC. Below about 600°C, oxidation is generally not a problem. Above 1000°C, the oxidation of both carbon and SiC are rapid. It is the temperature range of 600–1000°C that is the most difficult where the carbon oxidation can be rapid but the SiC is relatively inert [7.28]. Any microcracks or pores can allow ingress of oxygen for continued oxidation of the carbon.

Stress corrosion cracking (discussed in “Introduction” in

Chap. 8) of the matrix is a major problem in CMC. Another problem is that of oxidation embrittlement that can manifest

Copyright © 2004 by Marcel Dekker, Inc.